1. Field of the Invention
The present invention relates to a connecting structure for a vacuum double pipe that creates a vacuum between an inner pipe and an outer pipe, the vacuum double pipe, and a joint of the vacuum double pipe.
2. Description of the Related Art
In a conventional example of this type of connecting structure, a gap between an inner pipe and an outer pipe of a vacuum double pipe is sealed by flanges on either end to form an airtight space (see Japanese Patent Application Publication No. 2000-213675, for example). In the connecting structure described in Japanese Patent Application Publication No. 2000-213675, the flanges are disposed to face each other and connected by a ferrule clamp so as to connect respective inner pipes to each other, and a periphery of the inner pipe is sealed by packing on opposing surfaces of the flanges. A vacuum suction port is provided in the outer pipe, and by evacuating the airtight space between the inner pipe and the outer pipe into a vacuum through the vacuum suction port, the inner pipe and outer pipe are thermally insulated.
With the connecting structure described in Japanese Patent Application Publication No. 2000-213675, however, thermal conduction occurs between the inner pipe and the outer pipe via the flanges, and therefore a thermal insulation property between the inner pipe and the outer pipe deteriorates in a joint part including the flanges.
Further, in a vacuum double pipe described in Japanese Patent Application Publication No. 2000-213675, the space sandwiched between the inner pipe and the outer pipe is formed independently in each double pipe, and therefore evacuation must be performed on each double pipe individually. As a result, a large amount of labor is required to evacuate a plurality of vacuum double pipes to a vacuum.